Answer :

Distance covered by walking ⇒ 2.5*2 = 5km
Distance covered by running⇒ 10km
Total time taken⇒2+3= 5hrs
Total distance covered= 10+5=15km
Average speed=15/5= 3km/h
total distance =15 km

total time=5hrs

average speed= 15/5
                     =3km/hr